52 



BULLETIN OF THE 

 B — Teeth of the Lower Jaw, 



Skeleton. — Vertebral formula: Cervical vertebra?, 7; dorsal, 15; lum- 

 bar, 5; caudal (including the four sacral), variable; probable average, 16. 



Ten of the fifteen ribs articulate with the sternum ; their sternal por- 

 tions are entirely cartilaginous. Their osseous portions evidently increase 

 much in length after middle age. The apophyses of the vertebra} are 

 well developed. Of the neural spines of the dorsal vertebras, the first, 

 secondhand third are sub-equal, 130 mm. long; they gradually shorten 

 posteriorly, the last having a length of only 75 mm. 



The sternum is normally composed of nine osseous thick and broad 

 segments, the first and last very long, the eighth shortest. Between the 

 eighth and ninth a shorter cartilaginous one is sometimes intercalated (as 

 in specimen No. 2920). 



The pelvis (already fully described on pages 27- 29) is well developed. 

 The ilia are very long and narrow antero-posteriorly. The pubic bones 

 are unanchylosed, they being merely approximate at their posterior ex- 

 tremities. Probably in the females (as in Callorhinus ursinus), they are 

 widely separated, and the whole pelvis much smaller than in the males 

 and differently shaped. 



The humeri, as in the other Pinnipedes, are short and thick, with the 

 greater tuberosity enormously developed. The bones of the fore-arm are 

 also very -large and strong, with all their processes greatly developed; in 

 length they but slightly exceed the humerus. The length of neither of the 

 segments of the arm quite equals the length of the bones of the first digit 

 (including its metacarpal bone) of the hand. The first digit of the hand 

 is the longest, twice as long as the fifth, and very thick anil strong. 



The bones of the hinder limbs are also short and thick, especially the 

 femur, which is scarcely more than one third as long as the tibia. The 

 latter in length about equals the foot. The relative length of the digits 



* The distance from the crown to the alveolus, 

 t The portion inserted in the jaw. 

 J At the base of the crown. 



